Spark plug



O. C. ROHDE SPARK PLUG Fig. B

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Patented Aug. 15, 1933 SPARK PLUG Otto C. Rohde, Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio, a Corporation of Delaware Application February 25, -1932. Serial No. 595,093

4 Claims.

The object of this invention is to provide a spark plug in which the core of insulating material Y is less likely to crack than in spark plugs as heretofore made. When the core of a spark plug cracks under service conditions, it is usually caused by heat. In my improved construction such cracking is entirely prevented, or nearly so, by surrounding the central electrode by a metallic sleeve or bushing for at least a portion of the length of the core. The electrode is secured to this sleeve or bushing as Well as to the remaining portion of the core by cement which is forced in under pressure. This distributes the strain on the core, particularly near the inner or hottest end thereof, so that it is not likely to crack.

'Ihe invention will be more particularly explained in connection with the accompanying drawing in which Figure 1 is a central longitudinal section of a spark plug constructed according to the invention; Figure 2 is a similar view of the inner end of a spark plug having a modified form; Figure 3 is a perspective View of the sleeve or bushing; Figure 4 is an enlargement of the inner end of the core as shown in Figure 1.

As shown in the drawing the spark plug comprises a core 5 of insulating'material, preferably sillimanite, which is held in a metallic shell 6 in any suitable known manner. The outer or grounded electrode 7 is secured to the shell 6 and the other electrode 8 is secured in the core 5.

According to the invention a metallic sleeve or bushing 9, preferably split on one side as shown in Figure 3, is inserted into the inner end of the core 5 and extends from the extremity of the core through the portion which has heretofore been the most apt to crack from the heat. Cement 10 is then forced into the core and the sleeve 9 about the electrode 8 to secure the latter to the core. v The cap 11 is secured to the outer end of the spark 40 plug in any suitable manner.

The sleeve 9 is made from copper or other metal which is comparatively soft and pliable so that it will expand under the pressure of the cement and closely engage the core material at all points, so as 45 to distribute the strain when the spark plug is subjected to heat, but the sleeve will not be actually cemented directly to the core material. Any stresses occurring in the core, whether from unequal heating of the core itself or from the dif- 50 ference between its coeicient of expansion and that of the metal in the electrode, will be distributed so as to reduce to a minimum any tendency for the core to crack.

My invention of course is not limited to the .specific structure shown and described but in- (Cl. 12S-169) cludes all modifications which may fall within the scope of the appended claims.

What I claim is:

1. A spark plug comprising a core of ceramic insulating material, a thin sleeve of pliable metal respectively.

2. A spark plug comprising a core of ceramic insulating material, an electrode extending 1ongitudinally therethrough outer end portion thereof pliable metal around the and cemented to the and a thin sleeve of electrode within the inner portion of the core, said electrode being also cemented to the sleeve.

3. A spark plug comprising a core of ceramic insulating material, a split sleeve of thin pliable metal in the inner end of said core, and an electrode extending longitudinally through said sleeve and from end to end of the core, said electrode being cemented to the core and the sleeve,

said sleeve having a force fit Within the core.

4. A spark plug comprising a core of ceramic insulating material, an electrode extending longitudinally therethrough and cemented to the outer portion thereof, and a split sleeve around the electrode within the core, said electrode being inner portion of the also cemented to the sleeve with suicient cementI to expand the sleeve to a force flt within the c ore.

O'I'I'O C. ROI-IDE. 

